The present invention relates to a lighting device of a discharge lamp used for a headlight of an automobile.
There are conventionally known a lighting device of a discharge lamp which detects a short-circuit or an opening of the discharge lamp and forcedly stops lighting. As an example of such a lighting device of a discharge lamp, Japanese Unexamined Patent Application Publication No. 8-106986 discloses a device which detects a bulb voltage of the discharge lamp, determines occurrence of a short-circuit or an opening of the discharge lamp by comparing the detected voltage to a prescribed set value, and forcedly discontinues lighting of the discharge lamp.
In the conventional discharge lamp lighting device, however, a short-circuit of the discharge lamp is determined by means of the bulb voltage of the discharge lamp in the initial stage of lighting. Because the bulb voltage in the initial stage of lighting is unstable, however, an erroneous determination of short-circuit of the discharge lamp may cause stoppage of lighting. When conditions for threshold value to prevent erroneous determination are alleviated, occurrence of a short-circuit of the discharge lamp may sometimes be determined as being normal.
The present invention was developed to solve the problems as described above, and has an object to provide a lighting device of a discharge lamp which never stops lighting of the discharge lamp as a result of erroneous determination such as that of a short-circuit of the discharge lamp.
It is another object of the invention to provide a lighting device of a discharge lamp which, upon actual occurrence of a short-circuit, can ensure stoppage of lighting.
The present invention provides a lighting device of a discharge lamp, which lights the discharge lamp by feeding power to the discharge lamp, comprising a voltage detecting section which detects voltage impressed on the discharge lamp, and a lighting stop determining section which determines, on the basis of the voltage detected by the voltage detecting section, whether or not a short-circuit or a ground-fault occurs in a power feed line to the discharge lamp, and stops lighting in response to the result of the determination, wherein determination whether or not a ground-fault or a short-circuit occurs is not made for a prescribed period of time after dielectric breakdown of the discharge lamp or for a prescribed period of time after flow of a prescribed current to the discharge lamp. It is therefore possible to prevent an erroneous detection caused by use of an unstable bulb voltage in the initial stage of lighting.
The invention provides also a lighting device of a discharge lamp, further comprising an igniter which feeds an initial voltage for causing dielectric breakdown of the discharge lamp, wherein the igniter is arranged on the side of the discharge lamp not grounded in the initial stage of lighting; and the lighting stop determining section determines whether or not a ground-fault occurs on the igniter side of the discharge lamp before dielectric breakdown of the discharge lamp. The lighting stop determining section would therefore determine whether or not a ground-fault occurs in a voltage impressed on the non-grounded side of the discharge lamp before dielectric breakdown of the discharge lamp. Current resulting from ground-fault flows during a prescribed time of non-determination, and temperature of the circuit element through which the current flows increases and there is a change in resistance value. After the lapse of a prescribed period of time, the voltage detecting section detects a higher voltage. The invention thus permits prevention of the resultant impossibility to detect a ground-fault.
The invention provides also a lighting device of a discharge lamp, further comprising an igniter which feeds an initial voltage for causing dielectric breakdown of the discharge lamp, wherein the igniter is arranged on the side of the discharge lamp grounded in the initial stage of lighting; and the lighting stop determining section determines whether or not a ground-fault occurs on any or both of the terminals on the both sides of the discharge lamp before dielectric breakdown of the discharge lamp. The lighting stop determining section can determine whether or not a ground-fault occurs as to the voltage impressed on any one or both of the terminals of the discharge lamp before dielectric breakdown of the discharge lamp, in the lighting device of the discharge lamp in which the igniter is arranged on the side grounded in the initial stage of lighting from among the output terminals of the inverter. Current resulting from ground-fault flows during a prescribed time of non-determination, and temperature of the circuit element through which the current flows increases and there is a change in resistance value. After the lapse of a prescribed period of time, the voltage detecting section detects a higher voltage. The invention permits prevention of the resultant impossibility to detect a ground-fault.